Photoink printing



Oct. 27, 1936. E. N. BAKER PHQTOINK PRINTING Filed March 15-, 1933 new;fammfimr Patented Oct. 27, 1936 UNITED STATES PHOTOINK PRINTING Elton N.Baker, Chicago, Ill.

Application March 13,

4 Claims.

My invention relates to printing from plates produced by photographicprocesses and has more particularly to do with an improved method ofproducing planographic plates of this type.

An object of my invention is to provide a new and improved method ofproducing photo-ink planographic plates of either half-tone or linetype, which method will be simple, inexpensive, and efiicient to produceplates of excellent quality in a minimum of time and of sufiicientdurability to meet all ordinary requirements, which plates, if desired,may be used for the production of still more durable plates.

A further particular object of my invention is to produce such a processwhich is especially adapted for obtaining a plate directly on the mediumwhich is photographically exposed, there by avoiding loss of time andmaterial such as is encountered in indirect methods.

In its preferred embodiments, my invention is practiced byphotographically exposing in a camera, or by contact, a medium which forconvenience and economy may be a paper base coated with a silver-halideemulsion or colloid, or an ordinary photographic film having a similarcoating. After such exposure, which maybe in ordinary light or inartificial light, the image is developed on the base, which, hereafterin the specification and claims will be referred to as a detail inconnection with the drawing forming a part of this specification,wherein:

Fig. l is a plan view of a plate embodying my invention, and 1 Figs. 2-6inclusive, are sectional views of the same, on a greatly enlarged scale,at successive stages in the preparation thereof, the proportions as torelief being greatly exaggerated for purposes of clarity.

Figs. '7 and 8 are exaggerated sectional views of a plate embodying myinvention prepared by= alternative method steps.

. "Tl'ie" numeral I0 represents a base, which, as

stated above, is preferably of an inexpensive 1933, Serial No. 660,476

flexible material, such as paper or photographic film, and is coatedwith an emulsion 12 of silverhalide salt in a colloid such as gelatin orthe like. There is preferably provided an intermediate insulating layerl3 of baryta and gelatin.

(1) MAKING THE NEGATIVE The sensitized sheet, as shown in Figure 2, isexposed in the usual manner, preferably in a camera, to form a negative.ure 3,wherein the areas 15 of the layer l3 of photosensitive materialrepresent the areas which have been afiected by light, it will beunderstood that the sensitized sheet may be used to reproduce a drawing,photograph, sign, or any graphic 16' representation, or to reproducepictorially an original object or scene.

The negative medium used is preferably either paper or film or the likebecause of their fiexi bility and economy. Other inexpensive non- 20flexible media, however, may be used. The negative medium employedshould be of the process type to give extreme contrast adapted to therequirements of line and half-tone work. I The exposure and developmentof the negative is done in the customary manner but without the usualfixing operation. It is desirable that a nontanning developer beemployed, preferably a process developer yielding extreme contrasts. Aregulation acetic acid stop bath is convenient for stopping developmentat the proper time and for. neutralizing the alkaline condition of theemulsion as a result of development.

Spotting out pinholes and other retouching may be taken care of afterdevelopment. Filled lines or muddy whites may be cleared by a weakchromate bleach. Pinholes or weak blacks may be touched up with aconcentrated non-tanning developer. The negative is water rinsed andsqueegeed to remove excess water from the sur- 40 face before thisretouching.

I(2)-ETCHING n The exposed plate which has been develope but not fixedis subjected to an etching bath for the purpose of removing the'reducedportions l5 of the photosensitive coating 12. The etching operationresults in a plate somewhat as illustrated in Figure 4, the cavities I6representing the negative areas which have been etched out and theremaining portions I'I representing the posi-- tive areas of therepresentation.

This operation, as well as the remaining steps, can be carried out innormal light, althoughtoo active light action is not-preferable untilthis etch As shown in Fig- 10 length of time of etching.

used success- Water 32 ounces Copper sulphate crystals 2 ounces Nitricacid concentrated V3 ounce Potassium bromide crystals 15 grains Hydrogenperoxide (3% solution) Zounces Approximately one ounce of chrome alummay be added, if desired, to the above formula to prevent blistering ofthe paper.

Any chemical means of removing the colloid in exposed or reducedportions only, without removing the silver salts in the unexposed orunreduced portions, is in keeping with the general principles involvedin this process.

Theyetching action should be completed in from three to five minutes,using the above formula, although the time factor is subject toconsiderable variation, all within the control of the operator.

The etch leaves the gelatin underneath the exposed portions which havedissolved away in a spongy, soft condition, while the unetched areas areunchanged. A short water rinse with a forced water spray clears thesurface of adhering particles of gelatin as well as washing out most ofthe retained chemical of the etch bath.

In order to remove the chemicals completely -sirable:

Sodium bicarbonate 1 part (by weight) Water 16 parts (3) TANNING Thenegative image shouldnow be practically invisible and there should be avery decided relief visible.

Although it is not required, it is desirable, in order to produce arugged plate and one which will readily accept ink from a roller, toharden all the remaining gelatin by redevelopingin a tanning developerand then bleaching in a tanning bleach bath. A brief exposure of theplate" to a strong actinic light through the back as well as onto thesurface is sometimes of advantage when there is not a long lapse of timebetween tanning and etching.

- A. Redevelopment A tanning developer is used to redevelop the plate.The development will,,of course, give a much denser deposit of silver'in the unetched portions which may notbe obvious from surfaceexamination but is evident when looked at through the plate at a sourceof light. Too clean a background is not desirable; in fact, the bestplates frequently show a. denser black in the should not take longerthan thirty seconds with the following preferred developer:

A.Pyrogallic acid crystals 1 /2 ounces Water 8 ounces B.Sodium carbonate8 ounces Water 80 ounces For immediate use mix one part A with ten partsB.

(gher tanning developers may, of course, be use A brief water rinse isgiven, followed by immersion in a weak acid solution (citric acid ispreferred) to neutralize the alkalinity of the plate and to speed upelimination of the developer.

The redeveloped plate is indicatedin Figure 5 wherein the colloidcoating I8 has been partially hardened by redeveloping.

B. Bleaching The plate" is further tanned in a chromate bleach bath, forwhich either of the' following formulas is satisfactory:

Bleaching should be complete in about one minute, resulting in a platehaving a positive brown image with a background of lighter sepia tone.The surface of the plate should be quite tough and leathery.

The tanned plate is represented in Figure 6 wherein the numeral l9represents the tanned emulsion coating.

(4) INKING After being suitably mounted for stability, the plate can beinked up with a lithographic ink. Moisture applied to the plate firstwill dampen the background or etched portions and then ink will adhereonly to the image or unetched portions. l 1, being repelled by themoisture in the background in the same manner as with lithographicplates on stone and grained zinc or aluminum.

(5) PRINTING, on TRANSFERBING A. Direct printing At present, printingdirectly from the "plate" onto paper stocks suitable for lithographicprinting has been performed on a proof press of the cylinder impressiontype, manual dampening and inking being used. For'short runs, for whichthere is a definite commercial demand, this procedure is entirelypractical and profitable. However, the plate, may be well adapted tolonger runs on offset lithographic presses of the rotary type. This lastapplication is especially true of the small so-called office-device typeof offset lithographic press now on the market where the high cost andcomplicated process of platemaking is a decided disadvantage on-shortruns.

B. Transferring Ink transfers onto metal plates, by my method, can beused to secure either planographic or relief printing surfaces. Themethod of treating these ink impressions to secure either a resist forcellent results. The simplicity and economy of this new process ofmaking a master transfer, united with the simple transfer method,introduces a genuine practical short-cut in photo-v mechanicalprocedure.

ALTERNATIVE Eronmo BATH As an alternative embodiment of my invention, Imay use for the etching operation described above a bath of thefollowing type:

Water 10 ounces Ferric sulphate 1 ounce Hydrogen peroxide 1 ounce Whenusing this bath the reduced silver in the .kposed areas 20 (Figure 7) isnot reconverted to alight-sensitive silver-halide salt, as occurs whenusing a bath of the type described above. These negative areas 20 are,therefore, not sensitive to exposure and when a plate of .this type issubjected to redevelopment and tanning, as described above, the negativeareas 20 remain in a very porous condition wherein they accept watereven more readily than with the etch bath previously described. Thepositive areas of such a plate are represented by the numeral 2 l.

A plate of this type is found to be highly satisfactory, giving verysharp contrasts. Figure 8 represents such a plate after completion ofthe tanning step.

Various modifications and variations coming within the spirit of myinvention will doubtless suggest themselves to those skilled in the art.Hence, I do not wish to be limited to the precise form shown or usesmentioned, except to the extent indicated by the appended claims, whichare to be interpreted as broadly as the state of the art will permit.

I claim as my invention:

1. A process of preparing a printing plate, comprising photographicallyexposing a plate having a surface of colloid containing aphoto-sensitive silver salt and developing the plate to reduce theexposed silver salt, partially etching out the colloid containingreduced silver salt, thus leaving colloid on said areas, redevelopingsaid plate so as to reduce the remaining silver salts, and thensubmitting the plate to a chromate bleach bath to harden the surfacethereof, whereby to form a lithographic printing plate wherein theetched V portions will accept water and thus repel ink and the unetched'portions will accept ink.

2. A process of preparing a plate capable of printing on a printingpress with printer's ink, comprising photographically exposing a sheethaving a coating of.photo-sensitive-silver salt in a colloid carrier,developing said exposed sheet without fixing at the time, subjectingsaid sheet to an etch bath so as selectively to remove only portions ofthe colloid from the surface of areas which are to be non-printing andto produce there a water-accepting surface without substantiallyaffecting the ink accepting quality of the areas which are to beprinting areas.

3. A process of preparing a plate capable of' printing on a printingpress with printer's ink, comprising photographically exposing a sheethaving a coating of photosensitive silver salt in a colloid carrier,developing said exposed sheet without fixing at the time, subjectingsaid sheet to an etch bath so as selectively to remove only porl tionsof the colloid from the surface of areas which are to be non-printingand to produce there a water-accepting surface without substantiallyafiecting .the ink accepting quality of the areas which are to beprinting areas, and then hardening the entire remaininglcolloid.

4. A process of preparing a plate of a type which is a member of thegroup consisting of line and screen half-tone work, said plate beingcapable of printing on a lithographic printing press with lithographicink, comprising photographically exposing a sheet having a coating ofsilver halide in an emulsion of a suitable colloid, developing saidexposed sheet with a non-tanning developer, subjecting said exposedsheet to an etch bath so as selectively to remove those portions of thecolloid which contain the developed silver image, re-exposing to diffuseillumination, thereby making developable the hitherto unexposed silverhalide, and developing with a tanning developer, thereby producing aplate which will accept water upon the first exposed and etched areasand which will repel water and accept ink upon the unetched areas.

' ELTON N. BAKER.

